1. Field of the Invention
The invention relates to a planetary roller power transmission device. More specifically, the present invention relates to a planetary roller power transmission device that uses an oil-containing member to lubricate the interior of the device.
2. Description of Related Art
Conventionally, planetary roller power transmission devices have been used for a paper feeding mechanism of printers, for example, because rotational speed thereof is more uniform than that of planetary-gear-type power transmission devices, and power of motors can be transmitted with high precision. In a planetary roller power transmission device, power is sequentially transmitted by friction among a sun shaft, planetary rollers, and a stationary ring that are made of metal. As lubricant for preventing seizure of members due to friction between metals, grease is commonly used.
However, after a device has been used for a certain period, grease may leak from the device, whereby the grease may be depleted. If grease has been depleted, friction between metals is generated, which causes seizure to reduce the lifespan of the device. In view of this, it is proposed that an oil-containing roller formed by mixing synthetic resin powder with oil and baking the resulting mixture in a roller shape is used with grease to increase the lifespan of a device (see Japanese Patent No. 3104006 (JP 3104006 B), for example).
As depicted in FIGS. 7 and 8, a planetary roller power transmission device 50 described in the specification of JP 3104006 B includes a stationary ring 52, a sun shaft 53, a plurality of planetary rollers 54, and a carrier 55. The stationary ring 52 is fixed to a housing 51. The sun shaft 53 is disposed concentrically with the stationary ring 52 inside the stationary ring 52. The planetary rollers 54 are provided between the sun shaft 53 and the stationary ring 52 so as to be pressed against the sun shaft 53 and the stationary ring 52. The carrier 55 supports the planetary rollers 54 so that the planetary rollers 54 are rotatable and the carrier 55 rotates in conjunction with revolution of the planetary rollers 54.
Between the adjacent planetary rollers 54, oil-containing rollers 56 that are in contact with the planetary rollers 54 are each disposed. The respective oil-containing rollers 56 are rotatably supported by support shafts 58 provided so as to protrude on peripheral portions of a support body 57 that is provided at an end surface of the carrier 55 separately from the carrier 55.
As depicted in FIG. 9, between the adjacent support shafts 58 at outer peripheral portions of the support body 57, engagement recessed portions 60 are formed that engage with roller shafts 59 supporting the planetary rollers 54 so that the planetary rollers 54 are rotatable. These engagement recessed portions 60 each engage with the corresponding roller shaft 59, and thus the support body 57 can rotate concentrically with the carrier 55.
In the power transmission device 50, when the sun shaft 53 rotates, the planetary rollers 54 revolve while rotating, and the carrier 55 rotates along with this revolution. At this time, because the engagement recessed portions 60 of the support body 57 engage with the roller shafts 59 of the planetary rollers 54, the support body 57 rotates together with the carrier 55. The oil-containing rollers 56 supported by the support shafts 58 of the support body 57 revolve so as to follow the planetary rollers 54, and rotate while being in contact with peripheral surfaces of the planetary rollers 54. Accordingly, oil is supplied from the oil-containing rollers 56 to the planetary rollers 56, whereby oil films are formed on rolling contact surfaces between the planetary rollers 54 and the stationary ring 52. The oil-containing rollers 56 are supported by the support shafts 58, whereby positions thereof in the radial direction can be kept constant. Thus, the oil-containing rollers 56 are not caught between the stationary ring 52 and the planetary rollers 54.
In the power transmission device 50, the width of the engagement recessed portions 60 in the circumferential direction is larger than the diameter of the roller shafts 59, and thus the support body 57 can move by a certain angle in the circumferential direction with respect to the carrier 55. Consequently, the oil-containing rollers 56 supported by the support shafts 58 can move by the certain angle in the revolving direction with respect to the planetary rollers 54. Accordingly, the oil-containing rollers 56 rotate while being appropriately pressed against the planetary rollers 54, so as to supply oil to the planetary rollers 54.
However, in the conventional power transmission device 50, a clearance c (see FIG. 8) between the carrier 55 and the support body 57 is clogged with grease. This grease may cause the support body 57 to adhere to the carrier 55. If the support body 57 has adhered to the carrier 55, there are occasions when the oil-containing rollers 56 cannot be pressed against the planetary rollers 54. Specifically, if the support body 57 has adhered to the carrier 55, the support body 57 and the carrier 55 rotate together. Consequently, the oil-containing rollers 56 positioned by the support body 57 may continue revolving together with the carrier 55 while being positioned apart from the planetary rollers 54 in a non-contact manner as depicted in FIG. 10. In this case, oil cannot be supplied from the oil-containing rollers 56 to the planetary rollers 54, and thus the lifespan of the device cannot be increased.